The present invention is directed to a hammer drill in which a tool can be selectively imparted rotational force, impact force or a combination of rotational and impact forces by an impact force unit and a drive force unit with a drive motor for each of the units with the drive motors being independently controllable.
To achieve effective performance and long service life for a hammer drill of the type mentioned above, it is necessary to provide individual controllability of the revolutions per minute, the number of impact strokes and the strength of such strokes. Such a requirement occurs because of the different dimensions of the tools used as well as the type of material in which the hammer drill is employed.
In a known hammer drill, note the German Offenlegungsschrift No. 31 42 740, two drive motors are used each controllable independently of the other so that one drive motor operates the impact force unit and a second one operates the rotational force unit.
To assure that the hammer drill can provide the necessary performance in each type of operation, each drive motor is designed for the maximum performance for its respective type of operation and, as a result, relatively large drive motors are needed.